Naruto: The Outsider's Resolve - Chapter 1.6 (016):

Choi Hyun-seok, a heavyweight champion of the biggest mixed martial arts league on Earth and the one who was called the strongest had died.Afterwards, he was granted new life as a hero in another world.‘Wealth! Honor! Endless beauties at your fingertips!’With thoughts of such a dazzling future, the first thing that he saw when he came to this new world was a towering ox monster.The monster, who was the commander of the demon army, asked.“Hero? You’re saying you’re the hero?”“Uh…I think…?”And so, that was the start of hell.

Read at least six chapters, then prepare to crave the rest.The main character will show up in Chapter Five, though I don't recommend skipping the first four chapters.-----The world was celebrating. The Demon King was dead, along with his Darkness Generals.Humans led the other races to war for subjugation. They killed all, and none were spared. However, thousands of years before this happened, a piece of history was altered by time itself. In fact, the Demon King didn't have four generals but only one, which he sealed and sent into eternal slumber. Just as he started to close his eyes, the chains locked away for eternity shattered into pieces.

Cyril was a Harry Potter book fan. He unexpectedly obtained a chatterbox system that said it would take him to experience the desired Wizarding World.

He rubbed his hands together gleefully. Was there such a good thing?

However, once the system was finished, he found that this Wizarding World didn’t seem quite right?

Cyril (eyes shaking: Forest monster? Brass steam train? Gloomy wizard’s tower? Wizarding academy of the fittest? This wasn’t right!

System (forcing itself to be calm): Magic creatures! The appearance doesn’t matter! The architecture isn’t the key! It is still a wizarding academy! There isn’t anything wrong with it! Not bad, not bad!

Cyril struggled to make it through the Blackheart Wizard Academy. Fortunately, there was the gentle and courteous chief gentleman to cling to. This was until he found that the handsome chief seemed to be plotting against him…

My god! This seemed to the other identity of the crazy great magician and necromancer?

***

According to legends, the dark, paranoid, crazy and perverted great necromancer rubbed the white and delicate neck of the beautiful young man in his arms and whispered, “My dear, I heard that you have been very close to the commander of the Holy Light Knights recently?

Cyril denied it three consecutive times with an innocent face, “I’m not! I didn’t! Who is talking nonsense?”

- Description from Novelupdates